There Are More Stars Than Grains of Sand on Earth

A Mind-Boggling Number

Look at a handful of sand. Now imagine every beach and every desert on Earth. That's about 7.5 quintillion grains.

But the number of stars in the observable universe is even bigger: roughly 200 billion trillion.

How Do We Know?

Astronomers estimate there are about 200 billion galaxies in the observable universe. Each galaxy contains, on average, about 100 billion stars.

Putting It in Perspective

If you counted one star per second, it would take you about 6 trillion years to count them all. The universe is only 13.8 billion years old!

Counting the Uncountable

The comparison between stars and grains of sand is one of astronomy's most powerful illustrations of cosmic scale.

The Sand Count

Researchers estimated Earth's sand grains by calculating total sand volume and average grain size. Result: approximately 7.5 × 10¹⁸ grains.

The Star Count

The observable universe contains ~2 × 10¹¹ galaxies with ~10¹¹ stars each, totaling ~10²² to 10²⁴ stars.

JWST deep-field observations suggest the number could be even higher.

What About Planets?

The Kepler mission revealed that most stars have planets. Potentially 40 billion Earth-like planets exist in the Milky Way alone.

Key Points

• The observable universe is just a fraction of the total universe
• Every new telescope generation discovers more galaxies and stars
• The total universe could be 250 times larger (or infinite)

Stellar Census: Methods and Limitations

The comparison involves significant uncertainties in both quantities.

Estimating Stellar Populations

The number density of galaxies follows the Schechter luminosity function. The distribution of stellar masses follows the Kroupa IMF, where low-mass stars dominate — red dwarfs comprise ~75% of all stars.

JWST Revisions

JWST's deep-field observations have revealed galaxy counts at z > 10 that exceed predictions from ΛCDM models, leading to revised estimates suggesting 10²⁴ stars may be closer to the true count.

The Sand Calculation

Uncertainties in desert sand volumes alone could change the estimate by an order of magnitude.

Key Points

• Both numbers have uncertainties spanning 1-2 orders of magnitude
• The comparison remains robust: stars almost certainly outnumber sand grains by at least 10×
• Upcoming surveys (Roman Space Telescope, Euclid) will refine galaxy counts significantly